The present invention relates generally to photographic cameras and more particularly to an electromagnetic control device for driving the shutter of a camera.
Most known cameras employ spring operated lens shutters or focal plane shutters. Recently, an increasing number of electronic devices have found utilization in cameras particularly for the purpose of reducing the number of mechanical components necessary in forming the camera structure. In this course of development there has come into use a so-called "electrical shutter". In such a shutter, although the mechanical type of shutter timing device is replaced by an electrical circuit and magnetic winding device, the shutter blade drive mechanism has remained unchanged and utilization is still made of tensioned springs as the power source for driving the blades. Accordingly, a surveillance of the prior art will show that conventional shutter arrangements have not been sufficiently simplified and still maintain some degree of complexity in their structure and operation.
It has been known to provide electromagnetic control devices for actuating the shutter mechanism of a camera wherein a hollow bobbin having a magnetic winding thereon is formed as the movable part of a magnetic actuating assembly. A generally cylindrically shaped hollow yoke having a permanent magnet fixedly secured thereto is arranged in magnetically operable relationship relative to the bobbin. Generally, such a permanent magnet will have a pole piece at the top thereof with a guide shaft extending longitudinally from the center of the upper area of the pole piece. The internal surface of the yoke encloses a space extending about the external surface of the permanent magnet wherein magnetic flux is developed and within which the bobbin may be guided for axial movement in developing the actuating forces necessary to operate the shutter. As will be apparent, when the magnetic winding of the bobbin is energized a magnetic force is exerted which will interact with the magnetic force of the permanent magnet so that the bobbin will be moved in an appropriate direction. This magnetic force is utilized to control the opening and closing operation of the shutter. Generally, magnetic devices of this type will provide guide means in the form of a guide hole in the bobbin and a guide shaft in the yoke operating to effect guided movement of the bobbin relative to the yoke.
In order to enable the force of the magnetic actuating device to be balanced by the biasing force of a drive spring, conventional electromagnetic control devices must be formed with increased dimensions. Because of the generally annular construction of the armature, it is from a practical point of view very difficult to assure satisfactory efficiency of the electromagnetic control device within the small space available in applications such as a compact camera. Particularly, with a lens shutter which requires that the control device be positioned adjacent the photo-taking lens, problems of this nature can become quite serious.
Accordingly, the present invention is directed to the task of eliminating many of the conventional drawbacks in prior art systems and to providing an electronically operated magnetic control device for a lens shutter which is adapted for incorporation in a compact camera.
A further task to which the invention is directed is to enable the control device to be cooperatively adapted with the shape of the camera.
Furthermore, the invention is directed toward providing an electromagnetic control device having guide means which will make it possible to assure satisfactory operation of the shutter drive means.